1. Field of the Invention
The present invention relates generally to the chemical-mechanical polishing (CMP) technique. More particularly, the invention relates to a CMP method and a CMP apparatus which are preferably used for the planarization processes for substrates or wafer in semiconductor device fabrication.
2. Description of the Related Art
Recently, the CMP process has been attracting our attention as one of the planarization techniques in semiconductor device fabrication field. This is because the CMP process makes it possible to planarize globally a deposited film of films over a whole semiconductor wafer or substrate, which has been difficult to be realized with the use of any other conventional planarization techniques, such as the etch back process. The planarization of deposited film(s) is an essential process to enhance the integration scale (i.e., density) and miniaturization of semiconductor integrated circuit devices. Thus, it is said that the CMP process is one of the most important techniques.
FIG. 1 shows schematically a prior-art polishing apparatus for the CMP process.
The apparatus of FIG. 1 comprises a circular rotating platen 101 having a polishing pad 102 on its surface. The bottom of the platen 101 is fixed to a vertical rotating shaft 105. The shaft 105 is rotatable around its axis with a first driving mechanism (not shown). Thus, the platen 101 is rotatable in a horizontal plane by way of the shaft 105. The pad 102 is rotatable along with the platen 101.
A slurry supply tube 103 is mounted at a specific position over the platen 101 in such a way that the outlet of the tube 103 is oriented toward the pad 102. The tube 103 is used to supply a polishing slurry 104 onto the pad 102 in the form of drops.
A substrate holder 110 is movably provided over the platen 101 to hold or carry a substrate (e.g., a semiconductor wafer) 106 having a target film (not shown) to be polished on its surface. The holder 110 has a cylindrical body 111 with an inverted U-shaped cross section. The body 111 has a cylindrical inner space.
A vertical spindle 112 is fixed to the top of the substrate holder 111. The spindle 112 is rotatable around its axis with a second driving mechanism (not shown). Thus, the holder 101 is rotatable in a horizontal plane and movable vertically and horizontally by way of the spindle 112.
A circular plate 113 is fixed horizontally in the inner wall of the holder body 111. The plate 113 is located at an elevated position from the bottom end of the body 111 by a specific distance. A backing film 114, which is made of a resin, is attached to the lower surface of the plate 113.
The holder 110 holds or carries the substrate 106 by way of the backing film 114 and the plate 113. The holder 110 is horizontally rotatable and vertically movable with the second driving mechanism while holding the substrate 106.
Next, the operation of the prior-art polishing apparatus of FIG. 1 (i.e., the CMP process with the apparatus) is explained below.
First, a substrate 106 having a target film on its surface is held with the substrate holder 110 in such a way that the target film is oriented to the lower side. This is performed in the state where the holder 110 is sufficiently apart from the platen 101.
Next, a polishing slurry 104 is supplied onto the surface of the polishing pad 102 by way of the slurry supply tube 103 in the form of drops while rotating the platen 101 in a horizontal plane, as shown in FIG. 1. Due to the rotation of the platen 101, the slurry 104 supplied onto the pad 102 is automatically distributed uniformly on the surface of the pad 102.
Thereafter, the holder 110 is moved toward the pad 102 while rotating the holder 110 in the same direction as the rotating platen 101 until the target film (not shown) of the substrate 106 is attached to the surface of the pad 102. In this state, the surface area of the target film reacts chemically with potassium hydroxide (KOH) contained in the slurry 104, thereby forming a soft layer (not shown) on the target film. The soft layer thus formed is mechanically polished with grains contained in the slurry 104. As a result, the CMP process advances.
In this way, with the CMP process, the target film on the substrate 106 is polished by both a chemical action (formation of a soft layer) and a mechanical action (polishing with grains).
In general, the polishing rate (i.e., polishing speed) in the CMP process varies dependent upon various factors, such as the temperature of the polishing surface, the pressing force against the polishing pad 102, the backing pressure against the plate 113, the rotation speeds of the platen 101 and the holder 110, the surface roughness of the pad 102, the distribution status of the slurry 104, and the density of the grains in the slurry 104.
With the prior-art apparatus of FIG. 1, there is a problem that the polishing rate is likely to be non-uniform due to the above-describe factors in the polishing plane. For example, if the desired or designed polishing rate is 500xc2x150 nm/min, the actual polishing rate tends to have a dispersion as much as 50 to 100 nm/min over the whole substrate 106. To avoid this problem, a variety of improvements has been made so far.
For example, the Japanese Non-Examined Patent Publication No. 11-33897 published in 1999 discloses a polishing apparatus for CMP. This apparatus comprises temperature detection means for detecting the temperature of a substrate and substrate heating means for heating a substrate, which are located in substrate holding means for holding a substrate. The substrate is heated with the substrate heating means in such a way that the in-plane temperature of the substrate is uniform. This apparatus makes it possible to uniformize the temperature as one of the factors affecting the polishing rate over the whole substrate.
The Japanese Non-Examined Patent Publication No. 11-121409 published in 1999 discloses another polishing apparatus for CMP. This apparatus comprises heaters arranged concentrically in a top ring (i.e., substrate holding means). The heat quantities from the respective heaters are adjusted to control the in-plane temperature distribution of the substrate in the radial directions. This apparatus makes it possible to control the in-plane polishing rate of a substrate.
With the prior-art apparatus of FIG. 1, as explained above, the polishing rate (i.e., the polishing speed) is likely to be non-uniform within the polishing surface. Therefore, there is a problem that a satisfactory or sufficient flatness is difficult to be realized over the whole substrate. The insufficient flatness will cause exposure error due to discrepancy in depth of focus in the lithography process and/or reliability degradation of wiring lines formed over uneven surfaces.
With the polishing apparatus disclosed by the Publication No. 11-33897, the temperature may be uniformized over the whole substrate. However, any other factors affect the polishing rate. Thus, there is a problem that satisfactory flatness of the substrate is not always formed over the whole substrate.
With the polishing apparatus disclosed by the Publication No. 11-121409, there is a problem as follows.
In general, heat is generated by friction within the polishing period to thereby raise (or fluctuate) the temperature of the polishing surface. Like this, with the apparatus of the Publication No. 11-121409, there is a possibility that temperature fluctuation of the polishing surface occurs due to friction heat within the polishing period and as a result, a desired polishing rate or speed is unable to be generated. Therefore, a problem that satisfactory flatness of the substrate is not always formed over the whole substrate occurs.
Accordingly, an object of the present invention is to provide a polishing method and a polishing apparatus for CMP that uniformize substantially the polishing rate or speed within the polishing surface of a substrate.
Another object of the present invention is to provide a polishing method and a polishing apparatus for CMP that facilitate the generation of satisfactory or improved flatness over a whole substrate.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the invention, a polishing apparatus for CMP is provided, which comprises:
a polishing platen rotatable around its axis, on which a polishing pad is placed on operation;
a substrate holder for holding a substrate to be polished, the holder being rotatable around its axis and the substrate having a target film to be polished;
heating means for heating the substrate held by the holder;
temperature detecting means for detecting temperature of the heating means;
temperature compensating means for setting a temperature compensation value in such a way that a polishing rate is approximately uniform over a whole polishing surface of the target film; and
a controller for controlling the heating means in such a way that the temperature detected by the temperature detecting means corresponds to the temperature compensation value;
wherein the substrate is heated by the heating means while controlling the heating means with the controller within a polishing period of the target film.
With the apparatus according to the first aspect of the invention, there are provided with the heating means for heating the substrate held by the holder, the temperature detecting means for detecting the temperature of the heating means, the temperature compensating means for setting the temperature compensation value in such a way that the polishing rate is approximately uniform over the whole polishing surface of the target film, and the controller for controlling the heating means in such a way that the temperature detected by the temperature detecting means corresponds to the temperature compensation value. The substrate is heated by the heating means while controlling the heating means with the controller with the controller within a polishing period of the target film.
Thus, the polishing rate or speed can be substantially uniformized within the polishing surface of the substrate.
Moreover, the heating means is controlled by the controller in such a way that the temperature detected by the temperature detecting means corresponds to the temperature compensation value. Therefore, the generation of satisfactory or improved flatness can be facilitated over the whole substrate.
In a preferred embodiment of the apparatus according to the first aspect of the invention, the temperature compensating means sets the temperature compensation value based on post-polish thickness distribution of the target film. In this embodiment, there is an additional advantage that the polishing rate can be uniformized more surely.
In another preferred embodiment of the apparatus according to the first aspect of the invention, the heating means comprises heaters arranged to cover the substrate. The heaters are controlled by the controller.
In still another preferred embodiment of the apparatus according to the first aspect of the invention, the temperature detecting means comprises temperature sensors arranged to cover the substrate. Each of the sensors detects a temperature of a corresponding one of the heaters.
According to a second aspect of the invention, a polishing method for CMP is provided, which comprises:
providing a polishing platen rotatable around its axis, on which a polishing pad is placed on operation;
providing a substrate holder for holding a substrate to be polished, the holder being rotatable around its axis and the substrate having a target film to be polished;
setting a temperature compensation value in such a way that a polishing rate is approximately uniform over a whole polishing surface of the target film of the substrate; and
pressing the substrate held by the rotating holder against the rotating pad to polish the film while heating the substrate with heating means;
wherein the temperature of the heating means is detected by temperature detecting means;
and wherein the heating means is controlled in such a way that the temperature detected by the temperature detecting means corresponds to the temperature compensation value.
With the method according to the second aspect of the invention, due to the same reason as described for the apparatus according to the first aspect of the invention, the same advantages as those of the apparatus of the first aspect are obtainable.
In a preferred embodiment of the method according to the second aspect of the invention, a post-polishing thickness of the target film is measured. The temperature compensation value is determined based on the post-polishing thickness thus measured.
In another preferred embodiment of the method according to the second aspect of the invention, the heating means comprises heaters arranged to cover the substrate. The heaters are controlled by a controller.
In still another preferred embodiment of the method according to the second aspect of the invention, the temperature detecting means comprises temperature sensors arranged to cover the substrate. Each of the sensors detects a temperature of a corresponding one of the heaters.